1. Field of the Invention
The present invention generally relates to a semiconductor device.
Priority is claimed on Japanese Patent Application No. 2011-098446, filed Apr. 26, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
In a semiconductor device such as a DRAM (dynamic random access memory), in order to amplify minute signals read out from memory cells, sense amplifiers are provided for each bit line pair. When writing data into a memory cell, the sense amplifier performs a sensing operation that pulls one of the bit lines up to the high level and pulls the other bit line down to the low level. For this reason, high-level and low-level power supply voltages are supplied to the sense amplifier during the time of the sensing operation. In recent years, in order to pull the bit line that is pulled up to the high level more quickly to the high level, the overdrive method is used. The overdrive method is a method whereby, at the beginning of the sense operation period, an overdrive voltage that is higher than the high-level power supply voltage is supplied to the sense amplifier and, by adopting this method, it is possible to achieve a high-speed sense operation at the beginning of the sense operation.
Japanese Patent Application Publication No. JPA 2003-68073 discloses that, in a semiconductor device featuring the overdrive method, an overdrive voltage is supplied to the sense amplifier in response to the activation of an active command and a refresh command. The semiconductor device uses overdrive not only at the time of the active operation, but also at the time of the refresh operation. In the refresh operation, when there is no access (writing or reading) with respect the memory, current is consumed, and a large power consumption results.